1. Field of the Invention
The present invention relates to an optical scanner and an image forming apparatus.
2. Description of the Related Art
In recent years, there has been an increasing demand for higher speed optical scanners for use in optical printers such as laser beam printers, digital copiers, and plain paper facsimile machines. Conventionally, to improve the speed of an optical scanner using a single beam, the operating speed of a deflector is increased. This requires measures such as reducing noise due to high speed operation and increasing the output of the light source, resulting in a substantial increase in the production costs of the deflector.
Scanning multiple beams onto the scanning surface at certain pitch intervals in a sub-scanning direction has achieved high-speed scanning without increasing the rotational speed of the deflector. The multibeam scanning uses a circuit that modulates the plural light sources independently from each other. However, if a circuit board for light source modulation is provided for each of the light sources, an increased number of connectors and interconnect lines are used for connecting these circuit boards to a control circuit for generating write signals. Moreover, expensive cables for noise reduction such as shielded lines are used in addition to the circuit boards for the individual light sources. Adding these components significantly increases the production costs.
Japanese Patent Laid-Open Publication No. 2000-98278 discloses an inexpensive simple optical scanner capable of producing a beam spot on the scanning surface. In this optical scanner, plural light sources are mounted on a single circuit board such that light beams emitted from the respective light sources form an angle.
Optical scanners using semiconductor lasers need to achieve, as their optical properties, accuracy requirements of a laser beam position on the scanning surface, a main scanning direction of a laser beam, and a beam diameter in a sub-scanning direction. These accuracy requirements are becoming more stringent year by year.
The environment in which the optical scanners are actually used is inside a digital copier or a laser printer and, in many cases, is different from the environment in which adjustments of the optical properties of the optical scanners are performed. Therefore, tolerance of environmental changes, i.e., being less affected by environmental changes, is a feature required for the optical scanners.
Providing such an optical scanner having high accuracy and tolerance of the environmental changes leads to increased component costs due to improvements in the accuracy of the components of the optical scanner and increased time for assembly and adjustment due to more rigorous requirements in the adjustment accuracy. It is therefore difficult to satisfy such requirements in terms of both the scanning accuracy and the production cost.